Two-stroke piston-controlled engine



Sept. 24, 1946.' E. s. L. BEALE 2,498,030

l TWO STROKE PISTON-CONTROLLED ENGINE -Filed June 30, 1942 2 Sheets-Sheet l l. f25 30] I Evelqn Sew arf Ldnsdowneqlg mv E N Toe,

Sept. 24, 194s.

S TROKE PIS TON- CONTROLLED ENGINE VFiled June so. 1942 z .shegts-sheet 2 Patented Sept. 24, 1946 TWO-STROKE PISTON-CONTROLLED ENGINE Evelyn Stewart Lansdowne Beale, Staines, England, assigner to Alan Muntz & Company Limited, Hounslow, England, a British company Application June 30, 1942, Serial No. 449,078 In Great Britain June 26, 1941 (Cl. 12S- 51) 8 Claims.

The present invention relates to control of the rate of swirl of the charge in the working cylinder of a two-stroke internal-combustion engine of the kind in which the charge is admitted through ports to the radial direction is increased, i. e. as the ports are directed away from the centre of the cylinder. If the ports are shaped in the usual Way, that is with a constant angle along one or more ports controlled by a working piston, 5 the whole of their depth, the velocity'of the air and in which the position occupied by this piston passing through the ports is reduced as the area at the end of its out stroke and in consequence of port opening is increased, i. e` as the Stroke the maximum depth of port openings are variof the piston is increased, and the rate of swirl able. The invention is especially but not exdecreases correspondingly.

clusively concerned with compression-ignition According to this invention, in an engine of free-piston engines in which the stroke of the the kind specied, the shape of said port or piston varies with the load. ports is so varied along their depth that their -With internal-combustion compression-ignition mean directional eect on the charge flowing engines in which thegair charge to the working through them into the WOIkIlg Cylinder Varies cylinder is admitted through piston-controlled with the depth of port opening in such a manner ports cut in the cylinder walls, it is well known as to compensate, at least in part, for variation that if so-called tangential ports are used, that in the rate of swirl resulting from the change is ports the directions of which have components in the area of port opening due to variation in tangential to the cylinder, the air charge in the the position of said piston at the end of its out cylinder will be given a rotary movement. This stroke. Thus the angle of said port or ports to rotary movement is generally known as swirl and the radial direction may be increased along their will persist throughout the working cycle; when depth in the direction of the out stroke. Altera suitable rate of swirl is obtained a considerable natively, or in addition the width of said port or improvement occurs in the combustion of the ports may be decreased along their depth in the fuel. y direction of the out stroke.

The rate of swirl is controlled by the velocity Embodiments of the invention will be described of the air charge through the inlet ports, and vby wav of example, as applied t0 en air-00mby the angie which the ports make tc the radiai presser of the free-piston type, with reference direction. In the ordinary crankshaft engine, to the accompanying diagrammatic drawings, in Where the piston stroke is constant, the air charge 3o which: is also constant over the whole range of load. Fig. 1 is a sectional elevation of the com- Thus at any given engine speed the rate of swirl pressor, of the air charge is constant for all loads, since Fig. 2 is an elevation of a part of the appathe same volume of air passes through the same ratus shown in Fig. 1, to a larger scale, ports in a given time. Fig. 3 is a section on the line 3-3 in Figs. 1

In the case of a free-piston engine the piston and 2, stroke is not mechanically limited and varies Fig. 4 is an elevation corresponding to Fig. 2, with the load, and in particular there is a subbut showing a modified construction, stantial variation of the position of the pistons Fig. 5 is a section of a further modication, at the end oi their out strokes. With such Fig. 6 is a side elevation of the compressor engines it is desirable to obtain swirl of the air shown in Fig. 1, with part of the casing broken charge, and also it is desirable for this swirl to away, be nearly constant for all running conditions Fig. 7 is a section, the left-hand half being and independent of the position of the piston at on the line lL-'IL and the right-hand half on the end of its stroke. the line 'IR-'IR in Fig. 6,

As the area of port opening available for Fig. 8 is a part-sectional elevation of the part the entry of the air charge into the cylinder is of the working cylinder shown in Fig. i, with controlled by the piston, this effective port area a working piston in it, and is variable and dependent on the position of the Fig. 9 is a section on the line 9-9 in Fig. 8. piston at the end of its "out stroke. The quan- The air compressor shown in Fig. 1 has a. worktity of scavenge air available may also be variing cylinder I0 in which operate two opposed able and dependent on the'stroke of the piston. working pistons I I and I2. The piston I I is con- The rate of swirl in the cylinder is nearly pronected by a rod I3 to a compressor piston I4 operportional to the velocity of the air passing through ating in a compressor cylinder I5. The piston the ports and also increases as the angle of the I2 is connected by a rod I6 to a piston Il operating in a cylinder I8. The rods I3 and I6 are rigid respectively with cross pins I9 and 20 of the synchronizing linkage which constrains the two piston assemblies II, I4 and I2, Il to move at equal speeds in opposite directions. This linkage includes at one side of the compressor a lever 2| pivoted about a transverse axis at 22 and pivotally connected, at its ends respectively, by rods 23 and 24 to the pivot pins I9 and i; A similar lever 2 I, pivoted on a pin 22', and kpair of rods 23 and 24 (Figs. 6 and 7) are provided at the other side of the compressor, being so disposed that the two levers. 2l and 2| move oppositely. l

On the in strokes of the working pistons IIV and I2 the compressor piston Id draws in air through inlet valves such as 26 to thespaceon its left and at the same time delivers air on .its right through delivery Valves 21 to a scavenge-air receiver 30. On the out strokes of the working pistons the compressor piston I4 draws in air through inlet valves such as 25 to the space on its right and delivers compressed air on its left through delivery valves 2% through a discharge port 29 to a compressed-air receiver (not shown). The piston I'I and cylinder IB co-operate to form a compensating cushion which assists in moving the piston assemblies through their in strokes.

Exhaust ports SI in the working cylinder IEB are controlled by the piston I2 and communicate with an exhaust manifold 32. scavenge ports 53 in the cylinder IIB are controlled by 'the piston II and open directly into the space within the scavenge air receiver Sil. A fuel-injection nozzle is denoted by 34. The ends of the crosshead pins I9 and 2i) are fitted with slippers, such as 413 in Fig. '7, which slide in guide channels 4I cn the interior of the wall of the scavenge air receiver 3i).

The crosshead pin IS is connected by a link 42 and a crank i3 to an oscillatory cam M cooperating with the actuating member l5 of a fuelinjection pump IIS, the lobe of the cam being so sei*l that it actuates the pump ri to cause a delivery of fuel through a pipe 41 to the injection nozzle 3G. as the pistons approach their inner dead point. The pump l5 is provided with a slidable regulating member t3 coupled to a handle 49, whereby the quantity of fuel injected per cycle can be varied.

In this machine the inner dead point of the pistons is very nearly constant with varying load, for the following reasons. The diameters and clearance volumes of the compressor cylinder and cushion cylinder are so designed that the total energy of expansion from these two sources is very nearly constant, with the result that the total ener-gy of compression in the working cylinder must also be nearly constant The compression rises rapidly as the pistons approach the inner dead point, and therefore a small change in compression energy will cause only avery small displacement of the inner dead point. Since the compression characteristic is substantially constant, the expansion characteristic is determined by the quantity of fuel injected, and therefore the position of the outer dead point varies with the quantity of fuel injected, that is with the load, the stroke being substantially shorter at light loads than at full load. Figs. l, 6 and '7 show the pistons at their outer dead point under maximum load, while Figs. 8 and 9 show the position occupied by the piston II at the outer dead point under partial load.

This compressor, as so far described, is of Vknown type and operates in known manner. In

accordance with this invention, the scavenge ports 33 are shaped, as shown in Figs. 2,V 3, 8 and 9, in such a manner that their angle to the radial varies progressively along their depth, so as to compensate for the change in air velocity hereinbefore described. At the opening edge 35 of the ports (Figs. 2 and 3) their angle A to the lradial direction is a minimum, and this angle increases progressively until at the opposite edge 3% of the ports the port angle B approaches a tangential direction in relation to the cylinder,

asv shown by the dotted lines in Fig. 3, which show thesection ofthe ports at the plane A-A in Fig. 2; Consequently, when the stroke is short and only a small fraction of the total depth of the ports is uncovered by the piston near the edge 35, theaverage direction of that part of the port which is uncovered makes a relatively small ari-- gle to the radial, as will be clear from Fig. 9, where the full lines at the ports 373V show their section at the plane of the head of the piston II when vthis piston is at the outerdead point of such a reduced stroke, the angle of the ports to the radial at this plane being denoted by C, and the mean angle of the part of the port whichis uncovered'being denoted by Ms. As the stroke increases according to the load on the engine`so a larger fraction of the depth of the ports isexfposed by the piston and the average angleof 'the ports is increased up to the maximum angle `M1. (Fig. 3), and their mean directional effect on the air flowing through them varies accordingly. However, as the stroke is increased, the effective port area and the time available for the entry of the scavenge air are increased, and the velocity of the air through the ports is reduced as'described. This would reduce the rate of swirlif it were not for the fact that the average port angle is increased at the same time. By a proper choice of the angles of the ports along their depth the rate of swirl can be made practically constant, whatever the stroke of the piston. V

The direction of the air entering the rcylinder through a partly open port agrees more closely with the direction of the port as the ratio "of depth to width of the port opening increases. Consequently the width of the port may be varied, instead of or `in addition to its anglefover the depth of the port, in order to compensate for the change in area of port opening due to lvariation in piston stroke.

Fig. 4 shows scavenge ports 33A having a uniform angle to the radial throughout their depth, but decreasing progressively in width from the opening edge 35A to the opposite edge 36A.

In this connection another factor to be considered in thedesign is the'eifect of a lip on the opening edge of the port, sometimes used to prevent this edge of the port building up with carbonised oil. Such a lip is shown in Fig. 5 at 3,1 in a scavenge port 33B which is otherwise arranged as hereinbefore described with reference to Figs. 2 and 3 or to Fig. 4. With suche; lip` a, smaller rate of swirl is obtainedfor a given width of port at a given small fractional opening below the opening edge 35B, because the area ofthe port over the main part of its length is thenlar-ger in relation to thearea of the opening'into the cylinder, so that the air velocity along the port is relatively 10W, and therefore the direction@ the port has less influence on the direction of the air entering the cylinder. I 1 v The amount by which theanglelor the width of the port is varied is dependent' on the characteristics of each particular engine. It will be dependent on the variation of the stroke and also on the variation in the amount of scavenge air pumped through the ports with change of stroke.

While the invention has been described as applied to a free-piston engine, namely one in which the movement of a piston assembly or of an interlinked number of piston assemblies is controlled solely by the gas pressures acting on the several pistons, the invention is also applicable to other kinds of engines, such for example as a semi-free piston engine in which a piston assembly is controlled by an oscillating crank or the like which determines the inner dead centre of a working piston but wherein the position of the outer dead point is Variable with variation in the operating conditions.

I claim:

1. A two-stroke compression-ignition internalcombustion engine of the kind having a working cylinder, opposed pistons in said cylinder which is provided with scavenge ports and exhaust ports controlled respectively by said pistons, said scavenge ports being shaped to give a swirl to the charge admitted by them, synchronizing linkage connecting said pistons together for constraining them to move equally and oppositely, a reciprocating compressor having a compressor piston connected to one of said working pistons for reciprocation in unison therewith through strokes which vary with Variation in working conditions so as to vary the outer dead points of said working pistons and in consequence the maximum depth of port opening of said scavenge ports, wherein said scavenge ports are so shaped that the mean direction of the charge iiuid flowing through any one of said scavenge ports is nearer to the radial direction from the axis of said working cylinder at small port openings than at large port openings.

2. An engine as claimed in claim 1, wherein the angle of said scavenge ports to the radial direction is increased along their depth in the direction of the out stroke.

3. An engine as claimed in claim 1, wherein the width of said scavenge ports is decreased along their depth in the direction of the out stroke.

4. An engine as claimed in claim 1, wherein the angle of said scavenge ports to the radial direction is increased along their depth in the direction of the out stroke, and thel width of said scavenge ports is decreased along their depth in the same direction.

5. A two-stroke internal-combustion engine of the kind including a working cylinder having a tangentially directed scavenge port, a piston in said cylinder controlling said port, and means operable while said engine is running for Varying the position occupied by said piston at the end of its out stroke and in consequence the maximum depth of opening of said port by said piston, characterized in that the angle of said port to the radial direction increases along its depth in the direction of the out stroke, so that its mean directional effect on the lcharge flowing through it into said working cylinder varies with the depth of port opening in such a manner as to compensate, at least in part, for variation in the rate of swirl resulting from the change in the area of port opening due to variation in the position of said piston at the end4 of its out stroke.

6. A two-stroke internal-combustion engine of the kind including a working cylinder having a tangentially directed scavenge port, a piston in said cylinder controlling said port, and means operable while said engine is running for varying the position occupied by said piston at the end of its out stroke and in consequence the maximum depth of opening of said port by said piston, characterized in that the width of said port decreases along its depth in the direction of the out stroke, so that its mean directional effect on the charge flowing through it into said working cylinder varies with the depth of port opening in such a manner as to compensate, at least in part, for Variation in the rate of swirl resulting from the change in the area of port opening due to variation in the position of said piston at the end of its out stroke.

'7. A two-stroke internal combustion engine ofd the kind including a working cylinder having a tangentially directed scavenge port, a piston in said'cylinder controlling said port, and means operable While said engine is running for varying the position occupied by said piston at the end of its out stroke and in consequence the maximum depth of opening of said port by said piston, characterized in that the angle of said port to the radial direction increases along its depth in the direction of the out stroke, and the width of said port decreases along its depth in the said direction, so that its mean directional effect on the charge flowing through it into said Working cylinder varies with the depth of port opening in such a manner as to compensate, at least in part, for Variation in the rate of swirl resulting from the change in the area of port opening due to variation in the position of said piston at the end of its "out stroke.

8. YA two-stroke internal-combustion engine of the kind including a working cylinder having a tangentially directed scavenge port, a piston in said cylinder controlling said port, and means operable while said engine is running for Varying the position occupied by said piston at the end of its out stroke and in consequence the maximum depth of opening of said port by said piston, characterized in that the shape of said port varies along its depth in such a manner that its mean directional effect on a charge flowing through it into said working cylinder Varies by departing from the radial direction as the depth of port opening increases, so as to compensate, at least in part, for variation in the rate of swirl resulting from the change in the area of port opening due to Variation in the position of said piston at the end of its out stroke.

EVELYN STEWART LANSDOWNE BEALE. 

